Add thread safety annotations for some more PeerConnection members

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Add thread safety annotations for some more PeerConnection members
Plus all the annotations that were necessary to make things compile
again.
port_allocator_flags_ was accessed on both the signaling and the
network thread, but I was able to replace it with a return value.
Bug: webrtc:9987
Change-Id: Iab977a49d6588ce2240487475ec3588ae579caa1
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/128772
Reviewed-by: Steve Anton <steveanton@webrtc.org>
Commit-Queue: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27254}